Electric muffle furnace



Patented Sept. 25, 1934 UNITED STATES PATENT GFFlCE Application January Z7, 1933, Serial No. 653,852 In Germany January 4, 1932 1 Claim.

When using electrical energy for the heating of annealing and similar furnaces, and in view of the high cost of the electrically produced heat unit, it is important, especially in the case of 5 large furnace constructions, to reduce as much as possible the heat losses on the surface of the furnace and the heat required for raising the empty and cold furnace to its working temperature.

This necessity having been appreciated, it has already been proposed to replace the usual refractory-wall construction, unfavourable as regards heat economy in the above-mentioned sense, by a construction wherein the actual heat-radiating surface is constituted by a thin, light chamotte wall possessing little heat capacity, and reinforced or mechanically-strengthened by coiled-wire heating resistors embedded therein; the space between the said wall and the outer casing being filled with heat-insulating powder.

This method of construction with the use of thin self-supported charnotte plates, reinforced by the resistance wire is, however, difficult of application to the large types of inuiile furnace.

These disadvantages are eliminated by the method of construction according to the present invention, whilst in addition there is obtained the advantage that the undesirable heat capacity, the non-heat insulating parts of the furnace structure is further and substantially reduced.

The invention involves the use of heating resistance elements constituted by sheet-metal strips which are given a bowed, fluted, V or other channel cross section, to render the said elements inherently rigid and self-supporting and are interposed between refractory insulation and constitute a heat radiating surface covering practically the whole of a furnace wall.

Preferably the said strips are given an arch-like formation corresponding to the cross-section of the muflie chamber and are rendered mechanically rigid and self-supporting at all working temperatures by virtue of their channel cross section. They are adapted to constitute uniformly heat-radiating walls for the sides and roof of the Inutile chamber, and may be assembled to form a number of electrical resistances in series. Between the adjacent resistance strips there are interposed light ceramic insulations which serve as distance-pieces and insulate the several strips from contact with one another, whilst when only a heat-insulating powder surrounds the muffie chamber, the assembled system of electrical resistance elements and insulation prevents the said powder from entering the said chamber.

(Cl. 21S-35) An example of construction of a furnace constructed according to one application of the invention is shown in the drawing in Figure 1 in cross-section, and in Figure 2 in broken plan.

As shown in the drawing, the arched sheet G0 metal resistance elements l are given a curved or bowed cross-section so as to stiffen and render them self-supporting and to increase their heatradiating surface in relation to their width: the said elements however may be given a bowed, flutcd, V or other channel cross-section. Their ends rest on the furnace-hearth 2 and form the heat-radiating side-walls of the muflie 5.

The several resistance elements are separated by ceramic or other rigid refractory insulators 3 which also have a similar arched formation and may be made of the T-section as illustrated so that the assembly of resistor arches and refractory distance pieces will prevent the penetration of heat insulating powder 4 into the interior 5 of the furnace. The heating current may be supplied to the said resistance elements by connections G.

The said refractory arch shaped insulators may be supported with their ends only in the sides of the muiiled chambers, or they may be supported S0 by heat-resistors, which in this case are bearing their own weight as well as the weight of the furnace roof insulation.

Having described my invention what I claim and desire to secure by Letters Patent isz- J An electric muflie furnace wherein the heatradiating surface is constituted by a plurality of arch shaped strip metal resistor elements having a channel cross section and being supported by their ends resting en the sides of the muiile charnber, and arches of refractory material, arranged outside said elements, said refractory arches having inward projections whereby the said elements are insulated and located.

OTTO J UNKER. 

